Evidence for a dopaminergic dominance in the 4,α-dimethyl-m-tyramine-induced hypermotility in mice

Abstract

The effects of various drugs on the hypermotility induced in mice by 4,α-dimethyl-m-tyramine (H 77/77) was investigated.

The H 77/77-induced hypermotility was strongly inhibited by centrally acting dopamine-(DA-) receptor blockers (e.g., benperidol, fluspirilene, haloperidol) and potentiated by drugs increasing central DA activity by release of DA, by uptake inhibition (d- and l-amphetamine, nomifensine), or by inhibition of monoamine oxidase (e.g., parglyline, chlorgyline). While DA-receptor agonists (e.g., bromocriptine, ergocornine) potentiated hypermotility, the effects of those having a short duration of action (apomorphine, piribedil) were partly obscured. The catecholamine precursor L-dopa increased hypermotility only slightly, but its effect was markedly potentiated after inhibition of dopa decarboxylase.

Blockers of α- and β-adrenoceptors either did not affect H 77/77 hypermotility (e.g., WB 4101, pindolol) or inhibited it only at very high doses (e.g., phentolamine, propranolol). α-Adrenoceptor agonists (clonidine, guanfacine) had no clear effects.

No correlation was found between the H 77/77-inhibiting effect of antidepressant drugs and their ability to inhibit NA uptake.

Several antiserotoninergic compounds (pizotifen, 27-096, 29-245) blocked the effects of H 77/77, and a 65% drop in hypermotility was obtained after inhibition of 5-HT-synthesis with 6-flourotryptophan. Substances that increase central serotoninergic activity (l-5-HTP, fenfluramine), however, were inactive.

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